1. Field of the Invention
This invention relates to a chemical treating apparatus and a flow rate controlling method thereof, particularly to a chemical treating apparatus used in the manufacturing process of semiconductor devices, especially in the cleaning process, and a flow rate controlling method thereof.
2. Description of the Prior Art
As it will be stated below, there are two methods for treating (cleaning, etching, etc.) the face surface or the back surface of a substrate such as a semiconductor substrate, a quartz substrate, and the like.
(a) One method of chemical treatment is using an overflow type chemical treating apparatus 101, as shown in FIG. 1, in which the subject of treatment (for example, semiconductor wafer, glass wafer, etc.) 131 is placed in a main bath 111, and a liquid treating chemical 121in (shown by an arrow) is supplied to the main bath 111 from its bottom portion while the liquid treating chemical 121out (shown by an arrow) in the main bath 111 is discharged from the top portion of the main bath 111 into an outer bath 112 provided on the top periphery of the main bath 111.
(b) The other method is using a down-flow type chemical treating apparatus 102, as shown in FIG. 2, in which the subject of treatment (for example, a semiconductor wafer, a glass wafer, etc.) 131 is placed in a main bath 111, and a liquid treating chemical 121in (shown by an arrow) is supplied to the main bath 111 from an outer bath 112 formed on the top periphery of the main bath 111 while the liquid treating chemical 121out (shown by an arrow) in the main bath 111 is discharged from the bottom portion of the main bath 111.
In each method mentioned above, a liquid treating chemical 121 is supplied to a main bath 111 storing the subject of treatment 131 while the liquid treating chemical 121 is discharged to the outside of the main bath 111, wherein the adopted flow rate of the liquid treating chemical supplied ranges widely from a very small quantity to several dozens dm3/min. Generally, the optimum flow rate is set depending on the geometric shape of the main bath 111 and an outer bath 112, the subject of treatment 131 and the type of the liquid treating chemical 121 supplied. The set flow rate does not always have only one value; recent multi-functionalization in apparatuses has made it possible that more than one liquid treating chemicals are supplied alternately. In such a case, each time the type of liquid treating chemical is changed, the flow rate should be changed. Furthermore, even though apparatuses are designed so that the flow rate of a liquid treating chemical supplied is always constant during the supply, there are some cases where the flow rate variation during each supplying operation or the variation over a long time period exceeds a negligible level.
Further, in order to treat (for example, clean, wet-etch, etc.) the subject of treatment 131 uniformly, it is required that the liquid treating chemical 121 is sufficiently in contact with the face surface (or the back surface) of the subject of treatment 131 and that the liquid treating chemical 121 flows as laminar state as possible.
In the above-described overflow type chemical treating apparatus 101, regardless of the amount or variation of supply from the bottom portion of the main bath 111, the flow rate of the liquid treating chemical 121 in the main bath 111 is determined by the height of the wall of the main bath 111. Thus, unless the liquid treating chemical 121 is discharged from the main bath 111, the flow rate is stable irrespective of the amount of supply. Most of the conventional cleaning baths are overflow type ones which have such a structure that the liquid treating chemical 121 is supplied from the bottom portion of the main bath 111 and discharged to the outer bath 112. Therefore, the discharging capacity should be equivalent or exceed to the expected amount of supply. In addition, various discharging methods are applicable; that is, either the method using gravitation or the method using a pump is available. Therefore, variation of supply can be managed naturally by allowing the opening of the discharging port to have some extra area, for example.
On the other hand, in the above-mentioned down-flow type chemical treating apparatus 102, in order to keep the amount of the liquid treating chemical in the main bath 111 constant independent of the variation in the amount of supply of the liquid treating chemical 121 from the outer bath 112, it is necessary to discharge the same amount of the liquid treating chemical 121 as the amount of supply.
However, the conventional method which has been applicable to discharge a liquid treating chemical from the bottom portion of a main bath is either dropping the liquid treating chemical by gravity or discharging the liquid treating chemical with a pulsation pump. Therefore, the method for discharging a liquid treating chemical from the bottom portion of a main bath has been utilized only for the purpose of reducing the amount of the liquid treating chemical in the main bath or emptying the main bath. In such a conventional method, it is hard to allow the amount of discharge to be continuously variable and to control the amount of discharge according to the amount or variation of amount of the liquid treating chemical supplied from the outer bath. Specifically, since it is hard to discharge the liquid treating chemical from the main bath according to the amount of supply of the liquid treating chemical, the flow rate (the liquid level) of the main bath is not constant.
To be concrete, when the amount of the liquid treating chemical 121 supplied from the outer bath 112 is decreased from the liquid level 121A as shown in FIG. 7A, on which the liquid treating chemical 121 is held at a certain height higher than the side wall 111s of the main bath 111 and lower than the side wall 112s of the outer bath 112, to the level shown in FIG. 7B for example, the amount of discharge exceeds the amount of supply, and the amount of the liquid treating chemical 121 in the main bath 111 decreases. With the decrease, the liquid level 121A lowers, and when the level is lower than the upper end of the wall 111s of the main bath 111, the flow of the liquid treating chemical 121 around the subject of treatment 131 changes from the laminar state. In such a situation, the liquid treating chemical 121 dropping down the inner wall of the main bath 111 flows only in the neighborhood of the side wall 111s of the main bath 111. Furthermore, after the liquid level 121A reaches the subject of treatment 131, the upper portion of the subject of treatment 131 exposes from the liquid level 121A, which makes the treatment (for example, cleaning, etching, etc.) ineffective in such a portion.
On the other hand, when the flow rate of a liquid treating chemical 121in (shown by an arrow) supplied increases, as shown in FIG. 7C, the amount of discharge does not catch up with the amount of supply. Consequently, the amount of the liquid treating chemical 121 left in the outer bath 112 and the main bath 111 increases, and soon the liquid treating chemical overflows the outer bath 112.
When attempting a solution of the above problem using the prior art, as shown in FIGS. 8A and 8B, the attempt must be followed by opening and closing a valve for supply 141, a valve for discharge 142 or a pump (not shown in FIGS.). As shown in FIG. 8A, when the liquid level 121A of the liquid treating chemical 121 lowers with the decreasing amount of supply, the valve for discharge 142 is in closing action while the valve for supply 141 is in opening action. On the other hand, as shown in FIG. 8B, when the liquid level 121A of the liquid treating chemical 121 rises with the increasing amount of supply for the treating bath 110, the valve for supply 141 is in closing action while the valve for discharge 142 is in opening action. Although this method can keep the height of the liquid level 121A constant, in each case where the valve for supply or for discharge is in closing action, the action causes the flow of the liquid treating chemical 121 around the subject of treatment 131 to vary from the laminar state. In addition, it can cause the flow of the liquid treating chemical 121 to stop depending on the situation. This results in loss of efficiency in treating the subject of treatment.
Thus, the amount of the liquid treating chemical in the bath must be held constant by discharging almost the same amount of the liquid treating chemical as that of the liquid treating chemical supplied. In addition, abrupt changes in the amount of discharge caused by, for example, opening and closing the discharge port must be avoided.
The present invention provides a chemical treating apparatus and a flow rate controlling method thereof which are invented to overcome the above-mentioned problems.
Specifically, the chemical treating apparatus of the present invention is a down-flow type chemical treating apparatus in which a liquid treating chemical is supplied from the outside of a treating bath and discharged from the bottom portion of the treating bath, comprising a pump on the chemical discharging side of the treating bath which allows to discharge the liquid treating chemical to the outside of the treating bath substantially keeping the flow of the liquid treating chemical in the treating bath in the laminar state.
In the aforesaid chemical treating apparatus, a pump is provided on the chemical discharging side of the treating bath which allows to discharge the liquid treating chemical in the treating bath to the outside of the treating bath substantially keeping the flow of the liquid treating chemical in the laminar state: therefore, even when the liquid treating chemical in the treating bath is discharged by the pump, the flow of the liquid treating chemical in the treating bath is kept in the laminar state.
As a result, the liquid treating chemical is prevented from lowering to such a degree that the subject of treatment exposes from the liquid treating chemical, or rising to such a degree that the liquid treating chemical overflows the treating bath, which enables uniform and efficient treatment over the subject of treatment.
The flow rate controlling method of the chemical treating apparatus is a flow rate controlling method for a down-flow type chemical treating apparatus in which a liquid treating chemical is supplied from the outside of a treating bath and discharged from the bottom portion of the treating bath, comprising processes of detecting the amount of the liquid treating chemical supplied to the treating bath, and discharging almost the same amount of the liquid treating chemical as that of the liquid treating chemical detected.
In the aforesaid flow rate controlling method of the chemical treating apparatus, the process of detecting the amount of the liquid treating chemical supplied to the treating bath shows the amount of the liquid treating chemical supplied to the treating bath. The process of discharging almost the same amount of the liquid treating chemical as that of the liquid treating chemical detected allows the liquid treating chemical in the treating bath to be always constant in quantity, which makes it possible to prevent the liquid treating chemical from lowering to such a degree that the subject of treatment exposes from the liquid level or rising to such a degree that the liquid treating chemical overflows the treating bath.
The nature, principle and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by like reference numerals or characters.